Authorities in multiple counties in western Kentucky and northwestern Tennessee reported a mysterious gas-like odor Thursday morning, but the source of the stench is still unknown. Calloway County dispatcher Dan Galloway said the Sheriff's Office received anywhere between 15 to 20 calls of a natural gas smell.

The first call came from the Almo area at about 6:30 a.m. Galloway said Calloway County Fire-Rescue units responded to a residential area to find nothing. Minutes later, firefighters were called to the Dexter area for the same call. By later in the morning, Galloway said reports were coming in from most of the county as well as Marshall, Graves and Ballard counties in Kentucky and Henry and Stewart counties in Tennessee.

"We've talked to sheriffs' offices south of us and they have all reported the smell."

Calloway County Emergency Management Director Bill Call said officials have tested the air in multiple areas county wide to find no unusually high concentrations of natural gas or propane.

The Murray Natural Gas System has reported no leaks within the county. The municipal service runs 215 miles of natural gas pipelines in and around Murray and serves more than 7,000 residents, but Call said their systems would indicate a leak large enough to cause such a widespread smell.

As the morning progressed and calls kept flooding in, Call said officials considered whether the smell was weather related. A concentration of reports seemed to be coming from the Clarks River bottoms area, and Call said he wondered whether something thawing or rotting in that area was responsible for the smell. But as reports came in from miles and miles away, that was ruled out as well.

Galloway and Call said, for now, the only source they can imagine would be the Counce Containerboard Mill in Counce, Tenn. - just east of Memphis.

That's about 120 miles away from Murray, and unnamed officials with the mill said they have never heard of mill smells traveling that far, no matter how strong the wind.

For now, at least, the smell seems to have left the area, but the mystery remains, well, up in the air.

"We just don't know what it was, and I don't know if we ever will," Call said.